VARIATION BY USB AND DISUSE. 
257 
Those individuals of a species which have distinct 
points of advantage are most likely to survive; among 
runners the swiftest, among fighters the stoutest, and 
so on. Hence Professor Bailey applies the expres¬ 
sion, “ survival of the unlike.’’ 
He Yarigny gives an account of some experiments 
made upon common pond snails. Three young snails 
of the same brood were put into different vessels, 
containing five hundred, one hundred, and three hun¬ 
dred cubic centimeters of water respectively. Each 
snail was supplied with plenty of food. It was soon 
discovered that they were developing unequally ; the 
one in the largest vessel surpassed the others in size, 
and the one in the middle-sized vessel w^as larger than 
the one in the smallest. The conclusion was that 
the amount of water had something to do with the 
growth of the snail. 
De Yarigny doubted this conclusion, and began 
to experiment for himself. He put equal quantities 
of water into two vessels, one broad and shallow and 
the other spherical. The snails in the shallow vessel 
grew larger than those in the spherical one. He then 
put unequal quantities of water into two broad, shallow 
vessels, so that each had about the same water sur¬ 
face. The snails placed in them appeared to de¬ 
velop at nearly the same rate. He Yarigny observed 
that in the shallow vessels the snails spent much of 
the time swimming about at the surface of the water. 
He therefore concluded that the growth of the snail 
was due largely to the amount of exercise it took, and 
not to the volume of water in which it lived. 
